1) Field of the Invention
The present invention concerns a reactive carrier that forms no by-products during melt injection of polymer into articles such as sheets, films, fibers and containers. The reactive carrier is used to mix additives into the polymer resin. More particularly, the invention relates to the use of one or more cyclic anhydrides or substituted cyclic anhydrides as the reactive carrier. The polymer can be polyester or polyamide.
2) Prior Art
In many injection molded polymer articles additives are required to improve the functionality of the article. Typical additives are colorants, anti-slip agents, flame retardants, antioxidants, gas barrier agents, ultraviolet (UV) radiation absorbers, acetaldehyde reducing agents, crystallization control agents, fillers and the like.
A “masterbatch” approach has been used to mix additives into injection molded polymer articles. In the masterbatch process, the desired additive is dispersed at a relatively highly concentrated level within a carrier polymer. In a following process step, the masterbatch of highly concentrated additive polymer is blended with virgin polymer at the feed throat of the melt extruder. Depending on the quality of the process control of the drying and metering of the masterbatch, variations in additive levels and the polymer molecular weight can be unacceptable.
An alternative method is to use a liquid dispersion of the additive that is pumped at the extruder throat. The liquid carrier must be organic, non-aqueous, soluble in the polymer and have a boiling point greater than the extrusion temperature, i.e. generally above 300° C. Commercial liquid carriers can be obtained from ColorMatrix Corporation, Cleveland, Ohio and designated as ColorMatrix LCPY-1: 82-89 Series. According to the material safety data sheet (MSDS) from ColorMatrix Corporation, the main named ingredient is refined hydrocarbon oil.
The problem with the use of liquid carriers is that they can effect the processing of the article and remain in the article. For instance they can cause the extruder screw to slip, plate out on the molds and can be extracted.
U.S. Pat. Nos. 6,569,991, 6,573,359, 6,590,069 and 6,599,596 to Nichols et al. disclose the use of a reactive carrier that reacts with the condensation polymer, thereby binding the reactive carrier in the polymer resin and preventing the emergence of the carrier from the polymer resin during subsequent thermal processing. These patents show in the Figures the effect of the reactive carrier molecular weight on the theoretical loss of molecular weight for condensation polymers as a function of the concentration of the reactive carrier (i.e. use of the specified reactive carrier causes a loss of molecular weight of the polymer). High molecular weight (less than 10,000 g/mol) reactive carriers are preferred, especially polyols and most preferred polyethylene glycols with a molecular weight between about 400 and 1000 g/mol.
U.S. Pat. No. 6,342,578 to Huang discloses a polyester with one or more of phthalic anhydride, glutaric anhydride, benzoic anhydride, maleic anhydride or succinic anhydride in an amount sufficient to significantly reduce the caustic stress cracking. The anhydrides reacted with the hydroxyl end groups to form carboxyl end groups (CEG).
There is a need for reactive carriers that do not reduce the molecular weight of the polymer.